It is well known to those of ordinary skill in the art that automated systems for use in telecommunications applications typically require the capability of analyzing and identifying signals which are transmitted over a telephone network, such as, for example, the public telephone network in order to function properly. For example, it is well known that, under certain conditions, specific machine-generated single-frequency signals, denoted as "call-progress" signals, are transmitted over a telephone network to indicate call status conditions. Examples of commonly occurring call status conditions are busy, call-pickup, operator-intercept and so forth and examples of commonly occurring "call-progress" signals which are used to indicate these call status conditions include, without limitation, SIT tones (system intercept tones), answering machine tones, and so forth.
In addition to machine-generated single-frequency signals, it is also well known that automated systems for use in telecommunications voice processing applications require the capability of analyzing and identifying machine-generated communication signals such as ringback dial tone, dual tone multifrequency (DTMF) tones, and so forth as well as signals which are produced by human speech, noise and hum, and so forth. Such a capability of analyzing and identifying signals has many uses which are well known to those of ordinary skill in the art. For example, if an automated system places a call over the public telephone network to a predetermined telephone number, the automated system needs to have the capability of analyzing and identifying a whole host of signals which correspond, for example, to ringback, operator interception, human voice response to the telephone call, and so forth. In addition, because certain voice processing applications require a human to respond to queries with specific spoken responses, an automated system in such an application needs to have the capability of analyzing the signal produced by the human speech and of identifying the particular spoken response the called party gave.
In addition to the above-described need for an automated system to have the capability of analyzing and identifying signals, it is well known to those of ordinary skill in the art that it is desirable for the automated system to have the capability of analyzing and identifying signals rapidly so that the automated system can take an action which is an appropriate response to the identified signal.
In addition to the above-described need for an automated system to have the capability of analyzing and identifying signals rapidly enough for the automated system to provide an appropriate response to the identified signal, it is well known to those of ordinary skill in the art that the automated system advantageously should have the capability of analyzing and identifying signals which occur in analog signals as well as digital signals.
As one can readily appreciate from the above, there is a need in the art for method and apparatus for analyzing and identifying a signal which is produced by a human voice during telephone interactions with automated systems in telecommunications voice processing applications in order to distinguish that signal from: (a) specific single-frequency signals, i e., "call-progress" tones; (b) machine-generated communication signals such as ringback, dial tone, dual tone multifrequency (DTMF) tones, and so forth; and (c) noise, hum, and so forth. Further, there is a need in the art for method and apparatus for performing such identification rapidly enough that the automated system can take an action which is an appropriate response to the identified signal. Further, in addition to the above-identified needs, there is a need in the art for method and apparatus for performing such identification on on analog signals as well as on digital signals, whether the digital signals are digitally encoded by a differential encoding scheme or a non-differential encoding scheme such as a linear encoding scheme, a u-law encoding scheme, an A-law encoding scheme, a pulse code modulation (PCM) encoding scheme or so forth.